(a) Field of the Invention
This invention relates to an air flow rate measuring device for an internal combustion engine and in particular, although not exclusively, to a thermal type of air flow meter.
(b) Description of Related Art
A known thermal type air flow meter such as a so-called hot-wire air flow sensor is disclosed in Japanese Patent Application Laid Open No. 58-109817 (1983). The sensor disclosed therein has a metallic, cast, body defining a circularly cross-sectioned air intake main passage and a bypass, auxiliary air flow passage in which is located a hot wire and a temperature sensitive, compensating, resistor. The hot wire and the temperature sensitive resistor components are both connected to a circuit module adapted to drive these components and to process signals therefrom, the circuit module being located externally of the body. Also, as disclosed in Japanese Patent Application Laid Open No. 59-31412 (1984), it is known to locate the hot wire and the temperature sensitive resistor in an insulating molded housing for the circuit module.
Because, in the prior art, the construction is such that the circuit module protrudes outside from the intake air passage, there are problems such as difficulty in obtaining a convenient layout for the inside of the engine compartment, and there is also susceptibility to breakage of the circuit module.
It is an object of this invention to reduce the size and cost of an air flow rate measuring device. In a feature of this invention it is an object to provide improved thermal stability of the device.